This invention relates generally to a fluid dampening system, particularly for an offset printing press having at least one rotatable sprayer for spraying dampening fluid onto the first of a succession of dampening fluid transfer rollers.
A fluid dampening system having such a rotatable sprayer is disclosed in West German Pat. No. 2,439,999. Such a dampening system is employed for a rotary printing press, particularly a rotary offset printing press, for applying a wetting agent onto the printing plate of a print cylinder having a printing area and a non-printing area, the former being ink receptive and the latter being hydrophilic or moisture receptive. The apparatus according to the German patent has a plurality of such rotatable sprayers for spraying dampening fluid onto the surface of a roller included in the dampening system. Such roller transfers the dampening fluid to the printing plate for applying a film of moistening fluid to its surface which is retained by the hydrophilic area.
In order to assure that the dampening fluid is uniformly distributed onto the roller being sprayed, the spray issues through apertures located in confronting plates to meter the application of the dampening fluid to the roller, to thereby effect a relatively uniform application of the dampening fluid. Such uniformity is required if the printing plate is to be covered with a homogeneous film of the dampening fluid in the non-printing areas.
However, it has been shown that with the use of only such apertures it is not possible to apply the film of dampening fluid sufficiently uniformly and continuously to the printing plate as required for a given printing operation.
Also, a fluid dampening system employing rollers for applying a uniform film of the dampening fluid is disclosed in U.S. Pat. No. 3,168,037. Such a film dampening system, however, requires a relatively large number of rollers for applying the wetting agent sufficiently uniformly metered onto the printing plate.
Another fluid dampening system is disclosed in European Pat. No. 0,141,217 as having several fluid transfer rollers each with an elastic outer surface. However, such rollers do not simultaneously function as ink transfer rollers, such that it is difficult to achieve a suitable balance between printing ink and wetting agent in a short period of time.